1. Field of the Invention
The present invention relates to a signal processing method of an image signal. In particular, the present invention relates to a signal processing method of correcting an output signal from an effective pixel area by using an output signal from an optical black area (hereinafter referred to as an “OB signal”) of an image pickup part.
2. Description of the Related Art
An image device described in Japanese Unexamined Patent Application Publication No. 2002-335454 (hereinafter referred to as “Patent Document 1”) is conventionally known. The image device described in the Patent Document 1 (in particular, FIG. 1 and the paragraphs [0038] and [0084]) is provided with a structure such as an OB clamp section and a shading correcting section.
The OB clamp section uses an OB signal from an optical black area as a standard level of black to perform clamp correction on an output signal from an effective pixel area.
On the other hand, the shading correction section multiplies an output signal from the effective pixel area by a correction coefficient (fixed value) prepared in advance to correct shading occurring in the effective pixel area.
The inventor of the present invention has noticed a problem that noises such as black compression are likely to occur in an image when a signal is processed in the order of the OB clamp and the shading correction as in the conventional example described above.